JPH08298128A - Solid-state high polymer electrolytic fuel cell - Google Patents

Abstract

PURPOSE: To provide a fuel cell of high output having high open electromotive force and terminal voltage by forming an ion exchange membrane as a specific double layer ion exchange membrane, in the fuel cell forming the ion exchange membrane as a solid-state high polymer electrolyte. CONSTITUTION: An ion exchange membrane is formed as a double layer ion exchange membrane comprising at least three layers, anode side ion exchange membrane layer, ion exchange membrane layer containing a catalyst (example; platinum) of promoting reaction of producing H2 O from H2 gas and O2 gas to preferably have 0.1 to 500mg/cm<3> this catalytic amount and a cathode side ion exchange membrane layer. Further, water content of the anode side ion exchange membrane layer is preferably set larger than water content of the cathode side ion exchange membrane layer by 5 to 50wt.% particularly by 10 to 30wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art A hydrogen / oxygen fuel cell has been attracting attention as a power generation system that has a reaction product of only water in principle and has little adverse effect on the global environment. Above all,
Due to the rapid progress of research in recent years, the solid polymer electrolyte type has
High output density is possible, and it is highly expected that it will be put to practical use as a vehicle-mounted power source, etc., in addition to its features of small size and low temperature operation.

As the solid polymer electrolyte used in this application, a proton conductive ion exchange membrane having a thickness of 50 to 200 μm is usually used, and an ion exchange membrane made of a perfluorocarbon polymer having a sulfonic acid group is a basic characteristic. Has been widely and widely studied. In a solid polymer electrolyte fuel cell, gas diffusion electrode layers are formed on both sides of this ion exchange membrane, and hydrogen as a fuel and oxygen or air as an oxidant are supplied to an anode (hydrogen electrode) and a cathode (oxygen electrode), respectively. )
To generate electricity.

[0004]

In this case, hydrogen gas reacts at the anode, but a part of it is discharged unreacted out of the system, and a part of it further permeates the ion-exchange membrane to the cathode side. Leak. Similarly, part of the oxygen gas permeates the ion exchange membrane from the cathode side and leaks to the anode side. This phenomenon is called gas crossover, and the hydrogen gas or oxygen gas supplied to the electrodes and the oxygen gas or hydrogen gas leaking from the opposite side of the ion exchange membrane react on the electrodes to cause the operating potential of each electrode. Shift, causing a drop in cell voltage.

Further, there is a relation between the water content and the film thickness of the ion exchange membrane which is the electrolyte membrane, and the electrical resistance and the gas permeability. That is, the higher the water content of the ion exchange membrane, the smaller the electric resistance and the higher the gas permeability. The larger the thickness of the ion exchange membrane, the larger the electric resistance and the lower the gas permeability.

In order to increase the output of a solid polymer electrolyte fuel cell, the ion exchange membrane as an electrolyte is required to have a low electric resistance and a small crossover phenomenon due to gas permeation. None of the proposed ion exchange membranes satisfy these at the same time.

Conventionally, in order to suppress a decrease in cell voltage due to the crossover phenomenon, two ion exchange membranes are used as an electrolyte membrane, and a platinum catalyst layer is formed by sputtering between the membranes. A method of reducing the amount of gas reaching the electrode on the opposite side by reacting and consuming hydrogen and oxygen that permeate through the film in a layer (JP-A-6-10).
3992) has been proposed, but the performance is still insufficient.

[0008]

The present invention has been made to solve the above-mentioned problems. In a fuel cell using an ion exchange membrane as a solid polymer electrolyte, the ion exchange membrane is an ion exchange membrane on the anode side. A composite comprising at least three layers, a layer (1), an ion exchange membrane layer (2) containing a catalyst that promotes a reaction for producing water from hydrogen gas and oxygen gas, and a cathode side ion exchange membrane layer (3). Provided is a solid polymer electrolyte fuel cell, which is a layered ion exchange membrane.

In the multi-layer ion exchange membrane used in the present invention, when the water content of the anode side ion exchange membrane layer (1) is higher than the water content of the cathode side ion exchange membrane layer, it has particularly excellent performance. . In that case, the water content of the former is preferably 5 to 50% by weight, particularly 10 to 30%, as compared with the latter.
It is preferable to increase the weight percentage. On the other hand, the water content of the ion exchange membrane layer (2) is preferably equal to or higher than that of the cathode side ion exchange membrane layer (3). The water content of these ion exchange membrane layers (1), (2) and (3) is preferably controlled to 30 to 110% by weight, particularly 35 to 95% by weight.

In the present invention, the water content ΔW of the ion exchange membrane layer is defined as follows.

[0011]

[Formula 1] ΔW = (W ₁ / W ₂ −1) × 100 (wt%) W ₁ : 90 ° C., film weight after immersion in pure water for 24 hours, W ₂ : W1 is measured, then 100 ° C. The film weight after vacuum drying for 16 hours.

Hydrogen contained in the ion exchange membrane layer (2) formed between the anode side ion exchange membrane layer (1) and the cathode side ion exchange membrane layer (3) in the multilayer ion exchange membrane of the present invention. The catalyst that promotes the reaction of producing water from gas and oxygen gas is preferably a solid catalyst, and is a metal, a metal oxide, or a composite oxide. These are preferably 0.5
Although it is a fine particle of ˜500 nm, it is also used as a supported catalyst supported on an appropriate carrier.

As the carrier, carbon, metal oxide, complex oxide and the like are used. As the catalyst, a platinum group metal, an alloy thereof, an oxide, or a complex oxide, which has excellent catalytic activity and corrosion resistance under the use environment, is preferable. These catalysts are preferably dispersed in the ion exchange membrane layer (2) and are preferably present in a state of being covered with the ion exchange resin forming the ion exchange membrane.

In the present invention, in the ion exchange membrane layer (2),
The abundance of the catalyst is important, and the abundance of the catalyst (excluding the carrier when using a carrier) is 0.1 to 500 mg / cm ³ ,
Particularly, 1.0 to 250 mg / cm ³ is preferable. When it is smaller than the above range, the effect of adding the catalyst is small, while when it is large, the effect of adding the catalyst is not further increased, but on the contrary, the electric resistance of the ion exchange membrane layer is increased.

When the catalyst is the above-mentioned supported catalyst in particular, its bulk becomes a problem. Therefore, the amount of the catalyst in the ion exchange membrane layer (2) is 50% by volume or less, especially in the ion exchange membrane layer (2). Is preferably 30% by volume or less. When the amount is out of the above range, the ratio of the ion exchange resin in the layer decreases, so that the electric resistance increases and the output of the battery decreases.

The total thickness of the multi-layered ion exchange membrane of the present invention is preferably 30 to 300 μm, particularly preferably 50 to 250 μm. When it is less than the above range, the membrane strength and the handleability of the membrane such as electrode bonding are deteriorated, while when it is larger, the membrane resistance is increased and the output of the battery is decreased.

In the multi-layer ion exchange membrane, the ion exchange membrane layers (1), (2) and (3) do not have to have the same thickness. Rather, the anode side ion exchange membrane layer (1) is more preferably 5 to 20 than the cathode side ion exchange membrane layer (3).
It is preferable in terms of performance to have a thickness larger by 0 μm. on the other hand,
The intermediate ion exchange membrane layer (2) is made smaller than the above two layers, preferably 2 to 30 μm.

The ion exchange membrane layers (1), (2) and (3) constituting the multi-layered ion exchange membrane of the present invention are preferably made of a fluorocarbon polymer having a sulfonic acid group. As such a fluorocarbon polymer, CF ₂ =
CF ₂ and _{CF 2 = CF- (OCF 2 CFX} ) m -O q -
(CF _{2) n} -A (wherein m is an integer of from 0 to 3, n represents 0 to 1
A perfluorocarbon copolymer with a fluorovinyl compound represented by an integer of 2, q is 0 or 1, X is F or CF ₃ , and A is a sulfonic acid type functional group is preferable.

Preferred examples of the fluorovinyl compound include the compounds of Chemical formula 1 and the like.

[0020]

Embedded image CF ₂ ═CFO (CF ₂ ) _1-8 —SO ₂ F, CF ₂ ═CFOCF ₂ CF (CF ₃ ) 0 (CF ₂ ) _{1-8
-SO 2 F, CF 2 = CF} (CF 2) 0-8 -SO 2 F, CF 2 = CF (OCF 2 CF (CF 3)) 1-5 - (CF
₂ ) ₂ SO ₂ F.

In addition to the monomers constituting the fluorocarbon polymer, perfluoroolefins such as hexafluoropropylene and chlorotrifluoroethylene,
It is also possible to copolymerize perfluoroalkyl vinyl ether or the like.

The ion exchange membrane layers (1), (2),
The multi-layered ion exchange membrane composed of (3) can also be reinforced with a fibril-like, woven-like or non-woven-like fluorocarbon polymer.

The multi-layered ion-exchange membrane comprises an anode-side ion-exchange membrane layer (1), a catalyst-containing ion-exchange membrane layer (2), and a cathode-side ion-exchange membrane layer (3) which are separately formed into a film. Molded, preferably 120-23
It can be manufactured by adhering and stacking at 0 ° C. and 0.5 to 30 kg / cm ^{2 by a} hot pressing method or the like.

An ion exchange membrane layer (2) containing a catalyst is formed on one side of the anode side ion exchange membrane layer (1) or the cathode side ion exchange membrane layer (3) by a coating method, a spray method, a printing method or the like. After that, the other ion exchange membrane layer (3) or (1) is laminated so as to sandwich the above ion exchange membrane layer (2), and it can also be produced by a hot pressing method or the like.

A gas diffusion electrode is bonded to the surface of the multi-layered ion-exchange membrane according to a commonly known method, and then a collector such as carbon paper is attached. By sandwiching the multi-layer ion-exchange membrane having electrodes and current collectors on the surface, it is sandwiched between a pair of conductive chamber frames in which grooves serving as passages for fuel gas (hydrogen gas) or oxidant gas (oxygen gas) are formed. ,
It is assembled as a fuel cell.

The gas diffusion electrode used in the present invention is not particularly limited. For example, a porous sheet obtained by holding platinum-supporting carbon black powder with a water-repellent resin binder such as polytetrafluoroethylene can be used, and the porous sheet is coated with a sulfonic acid type perfluorocarbon polymer or a polymer thereof. Fine particles may be included. This porous sheet is bonded as a gas diffusion electrode to the ion exchange membrane, which is a solid polymer electrolyte, by a hot pressing method or the like.

In another example, platinum-supporting carbon particles and a sulfonic acid-type perfluorocarbon polymer are formed on both sides or one side of a carbon paper or the like forming an ion exchange membrane or a current collector by a coating method, a spray method or a printing method. An ion exchange membrane having an electrode layer on the surface thereof is formed by forming a layer of a gas diffusion electrode comprising a mixture of the above and adhering them by a hot pressing method or the like, preferably at 120 to 350 ° C. and ^{2 to} 100 kg / cm ² . Alternatively, a current collector can be manufactured.

Next, the current collector or the ion exchange membrane layer is bonded to the ion exchange membrane layer or the current collector, respectively.

[0029]

In the present invention, a fuel cell excellent in terms of open electromotive force and terminal voltage can be obtained, and its mechanism is considered as follows. In a polymer electrolyte fuel cell using an ion exchange membrane as an electrolyte, chemical energy is converted into electric energy according to the following reaction.

[0030]

Embedded image Anode: H ₂ → 2H ⁺ + 2e, cathode: 1 / 2O ₂ + 2H ⁺ + 2e → H ₂ O.

The hydrogen gas and oxygen gas used in the above reaction move in the ion exchange membrane toward the cathode and the anode, respectively, due to the crossover phenomenon, and react on the electrodes to lower the cell voltage. cause. In the present invention, since the multi-layered ion exchange membrane has the ion exchange membrane layer (2) as the intermediate layer, the crossover phenomenon can be prevented without deteriorating the membrane performance.

That is, in the present invention, it has been found that the catalyst for preventing the above-mentioned crossover phenomenon does not need to be present in a large amount in the ion exchange membrane, and the catalyst such as platinum group metal to be used as the catalyst is in a dispersed state. Moreover, since it exists in the ion exchange membrane layer (2) in a state of being covered with the ion exchange resin, the crossover phenomenon can be prevented without substantially hindering the migration of protons passing through the ion exchange membrane.

In order to prevent the above-mentioned crossover phenomenon which does not hinder the movement of protons in the present invention, also when the water content of the ion exchange membrane is increased and the permeability of hydrogen gas and oxygen gas in the ion exchange membrane is increased. It turned out to be achievable. Thus, in order to compensate for the relatively low water content compared to the ion exchange membrane layer (3) on the cathode side of the ion exchange membrane, which has a high water content state due to the water generated by the reaction, the water content on the anode side is high. A multi-layer ion exchange membrane having the ion exchange membrane layer (1) having

By these, it becomes possible to prevent the crossover phenomenon and to satisfy the contradictory characteristics of high proton mobility and low electric resistance, and as a result, high output of the fuel cell is achieved.

[0035]

EXAMPLES Specific embodiments of the present invention will be described below with reference to Examples (Example 1,
Examples 3 and 5) and comparative examples (Examples 2 and 4) will be described, but the present invention is not limited thereto.

[Example 1] CF ₂ = CF ₂ and CF ₂ = CFO
Ion exchange capacity consisting of a copolymer with CF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F 1.1 meq / g dry resin and 1.0 meq / g dry resin I prepared a coalesce. The former copolymer was extrusion-molded at 220 ° C. to obtain a film (1) having a thickness of 45 μm. Next, the latter copolymer was extrusion-molded at 220 ° C. to obtain a film (3) having a thickness of 45 μm. Furthermore, the former copolymer is 40%
Platinum-supporting carbon black powder was added at a ratio of 10% by volume and kneaded to form an extrusion film at 220 ° C., and a thickness of 20 μ
A film (2) having m and a platinum content of 25 mg / cm ³ was obtained.

The above three types of copolymer films (1),
220 (2) and (3) with the film (2) in the center
Laminated using rolls at ℃, dimethyl sulfoxide 30
It was hydrolyzed in a mixed aqueous solution of 15% by weight of potassium hydroxide and 15% by weight of potassium hydroxide, washed with water, and then immersed in 1N hydrochloric acid.
Next, the laminated membrane was washed with water, its four sides were restrained by dedicated jigs, and then dried at 60 ° C. for 1 hour to obtain a multilayer ion exchange membrane. The water contents of the copolymer films (1) and (2) and the copolymer film (3) in pure water at 90 ° C. were 70% by weight and 50% by weight, respectively.

The above-mentioned multi-layered ion exchange membrane was incorporated into a gas permeability measuring cell made of PTFE (polytetrafluoroethylene), the cell was kept warm at 85 ° C. by a heater, and the copolymer film (1) side was saturated at 85 ° C. Normal pressure hydrogen moistened with steam was supplied, and normal pressure inert gas or oxygen moistened with saturated steam at 85 ° C. was supplied to the side of the copolymer film (3) to leak into the inert gas or oxygen. The amount of hydrogen was measured by gas chromatography. The permeation amount of hydrogen when the inert gas was supplied was 0.27 microliter / cm ² / sec, whereas the permeation amount of hydrogen when oxygen was supplied was 0.021 microliter / cm ² / sec, Hydrogen permeation decreased.

Example 2 1.1 milliequivalents used in Example 1 /
g A copolymer of dry resin was extruded at 220 ° C to form a film having a thickness of 6
A film of 5 μm was obtained.

This film and the ion exchange capacity 1.0 meq / g dry resin copolymer film (3) used in Example 1 were laminated at 220 ° C. using a roll, and this was laminated in the same manner as in Example 1. A multilayer ion exchange membrane was obtained by hydrolysis, immersion in hydrochloric acid, washing with water, and drying. With respect to this multilayer ion exchange membrane, the amount of hydrogen permeation of gas was measured by the same method as in Example 1. There is no change between the supply of inert gas and the supply of oxygen, and the permeation amount of hydrogen is 0.29 microliters /
It was cm ² / sec.

Example 3 A gas diffusion electrode comprising 60 parts by weight of carbon black and 40 parts by weight of PTFE on both sides of the multilayer ion exchange membrane used in Example 1 and having a thickness of about 200 μm.
Platinum-supported gas diffusion electrode (platinum-supported amount 0.5 mg / cm
² ) was joined by a hot pressing method under the conditions of a temperature of 150 ° C. and a pressure of 10 kg / cm ² for 10 seconds.

The multi-layered ion-exchange membrane was incorporated into a cell for measuring battery performance so that the copolymer film (1) side was the anode side and the copolymer film (3) side was the cathode, and an open electromotive force and power generation were performed. The performance was measured. The results are shown in Table 1.

[Example 4] Gas diffusion electrodes were bonded to both surfaces of the multilayer ion-exchange membrane used in Example 2 in the same manner as in Example 3.
The multi-layer ion-exchange membrane has a 1.1 meq / g dry resin copolymer film side on the anode side, while an ion exchange capacity of 1.0 meq / g dry resin copolymer film side is on the cathode side. It was incorporated into a cell for battery performance measurement, and the open electromotive force and power generation performance were measured. The results are shown in Table 1.

Example 5 Copolymer film (3) of the ion exchange capacity of 1.0 meq / g dry resin used in Example 1
A sandwich of the copolymer film (2) used in Example 1 between two sheets was roll-pressed at 220 ° C. to give Example 1
A multilayer ion exchange membrane was obtained by the same treatment as above. Gas diffusion electrodes were bonded to both surfaces of this multilayer ion exchange membrane in the same manner as in Example 3. By incorporating this into a cell for measuring battery performance, open electromotive force and power generation performance were measured. The results are shown in Table 1.

The battery performances of Examples 3, 4 and 5 were measured under the same conditions with a cell temperature of 70 ° C. and humidified hydrogen and air supplied to the anode and cathode, respectively. The terminal voltage shows a value at a current density of 0.5 A / cm ² .

According to Table 1, Example 3 containing the ion-exchange layer (2) in the multilayer ion-exchange membrane has a higher open electromotive force than Example 4 not having the ion-exchange layer (2) and has a high water content on the anode side. Example 3 having the ion exchange membrane layer of No. 2 has a higher terminal voltage during power generation than Example 5 having the ion exchange membrane layer having the same water content on the anode side and the cathode side.

[0047]

[Table 1]

[0048]

EFFECT OF THE INVENTION The solid polymer electrolyte fuel cell of the present invention has an increased water content due to water produced by the reaction of hydrogen gas and oxygen gas in the ion exchange membrane layer (2), and the ion exchange membrane layer on the anode side. Due to the high water content of (1) and the increase of the water content due to the water originally generated at the cathode, the entire multi-layer ion-exchange membrane has a high water content, so that the amount of protons transferred through the membrane is large and the high opening rate. Not only can a high output having electric power and terminal voltage be achieved, but since the ion exchange membrane is always kept at a high water content, it is less susceptible to changes in humidity in the external environment, and the fuel cell operation becomes easier.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuji Shimohira 1150 Hazawa-machi, Kanagawa-ku, Yokohama, Kanagawa Prefecture Asahi Glass Co., Ltd. Central Research Laboratory

Claims (3)

[Claims] 1. In a fuel cell using an ion exchange membrane as a solid polymer electrolyte, the ion exchange membrane promotes a reaction of producing water from hydrogen gas and oxygen gas with an anode side ion exchange membrane layer (1). A solid polymer electrolyte fuel cell, which is a multi-layer ion exchange membrane comprising at least three layers of a catalyst-containing ion exchange membrane layer (2) and a cathode side ion exchange membrane layer (3). 2. The amount of catalyst in the ion exchange membrane layer (2) is 0.
The solid polymer electrolyte fuel cell according to claim 1, which has an amount of 1 to 500 mg / cm ³ . 3. The water content of the anode side ion exchange membrane layer (1) is 5 more than the water content of the cathode side ion exchange membrane layer (3).
The solid polymer electrolyte fuel cell according to claim 1 or 2, which is larger by 50% by weight.